Download BUNT OF WHEAT

1. COMMON BUNT/ HILL BUNT/ STINKING BUNT/
COVERED SMUT OF WHEAT
ETIOLOGY:
1. Low Bunt: Tilletia caries (syn. Tilletia tritici)
2. High Bunt: Tilletia laevis (syn. Tilletia foetida)
3. Dwarf Bunt: Tilletia contraversa (syn. Tilletia calospora)
SYSTEMIC POSITION:
Class: Basidiomycetes
Order: Tilletiales
Family: Tilletiales
INTRODUCTION:
 The name “Bunt" comes from a dialectic contraction of the term "burnt ears" to "bunt ear" and finally to just
"bunt."
 Distributed throughout the world. Mainly confined to cooler regions. In Nepal they are found in high hills at or
above 6000ft, so called Hill bunt.
 During late 1970s, disease was serious problem in Dolkha and Solukhumbu, latter in Salyan and Rolpa.
 The disease is capable of causing heavy losses in grain yield, which range from negligible to complete loss of the
produce. Besides yield losses, it causes a serious deteriration in wheat flour.
 It imparts a fishy odour and black colour to the wheat meal resulting in the unpalatable chapatis.
SYMPTOMS:
1. The fungus attacks seedling of 8-10 days old and become systemic and grows
along the tip of shoot. The disease is not usually visible until heading stage.
2. After heading, the spikelets of infected plants tend to "flare-out" and take on a
greasy, off-green color. This "flaring out" of the spikelet is due to the
expansion in size of the bunt infected seed that has become filled with
teliospores.
3. Infected plants ripen earlier than the healthy and the ears are dark green
4. The infected culm is shorter than healthy when attacked by T. caries whereas it
remains the same height in T. foetida attack
5. In place of normal seeds, infected kernels develop into “Bunt balls"
6. Inside of the grain is filled with greasy black spore mass smelling fishy like
rotten fish in the field due to Trimethylamine.
Fig 2: Common bunt “Bunt balls" within
wheat seed coats.
Fig 1: Stinking Bunt with Flaring out spikelet
Fig 3: Dwarf bunt
LIFE-CYCLE:
Tilletia sp. is externally seed borne. When infected seeds are sown, spores on the seed born along
with the seedling. Each produces a short fungal thread terminating in a cluster of elongated cells.
These then produce secondary spores which infect the coleoptiles of the young seedlings before the
emergence of the first true leaves. The mycelium grows internally within the shoot infecting the
developing ear. Affected plants develop apparently normally until the ear emerges when it can be
seen that grain sites have been replaced by bunt balls. Spore mass can survive for 25 years under dry
condition.
Fig 4: Life Cycle of Common Bunt of Wheat
SURVIVAL AND SPREAD:
Primary source of inoculum: Teliospores
• Teliospores are smooth walled measuring 22-49μ in diameter and require a
long resting period.
• Teliospores germinate and produce a large number (60-120) of needle shaped
primary sporidia on a short stout basidium.
Favourable conditions:
•
•
•
•
Moderate temperatures (19-23°C),
High Soil Moisture (> 15%),
High humidity (>70%) and
Cloudiness or rainfall during anthesis favors disease development in
susceptible host varieties.
2. KARNAL BUNT OF WHEAT
ETIOLOGY: Tilletia indica. T. barclayana, Neovossia indica
SYSTEMIC POSITION:
Class: Basidiomycetes
Order: Ustilaginales
Family: Tilletiaceae
INTRODUCTION:
• Karnal bunt was first discovered in 1930 in Karnal, India by Mitra in 1931 , from which it
gets its name.
• Karnal Bunt is sometimes called partial bunt because only few kernels in a spike usually are
affected making the disease much less conspicuous than other bunts where whole ears are
infected. Overall infection rates are less than 1 percent.
• Karnal bunt of wheat has become a major issue in the wake of Sanitary and Phytosanitary
(SPS) Agreement stipulated by WTO. Under the agreement, each member country must
undertake a pest risk analysis (PRA) for all agricultural commodities for export and import.
SYMPTOMS:
 The infection is usually confined to a few grains in the spike with irregular arrangement.
 Karnal bunt is first visible at the soft-dough stage in the form of blackened areas surrounding the base
of the grain.
 In severe cases, the grain is reduced to black shiny sac of teliospores.
 As the grains mature the outer glumes spread and the inner glumes expand, exposing the bunted
grains.
 The bunt affected plants emits a foul smell which is mainly due to the presence of Trimethyl amine.
 There may be a slight swelling or darkening of infected florets.
Fig 5: Karnal Bunt in Wheat Grains and Spikelets
LIFE-CYCLE:
The disease produces three types of
spores. Teliospores are found on or
in the soil. When they germinate
they produce primary sporidia. These
spores may be blown by wind or
splashed by rain onto wheat plants.
When primary sporidia germinate
they produce secondary sporidia—
the spores that germinate and
penetrate the wheat glumes. Mycelia
grow down to the base of the glumes
and up into developing kernels.
Masses of black teliospores then
develop in infected kernels. The
fungus infects one or more
developing seed on a head, but
usually not all the seed. Large
numbers of teliospores must be
present to cause reliable infection.
FIG 6: LIFE CYCLE OF KARNAL BUNT OF WHEAT
SURVIVAL AND SPREAD:
Primary Spread of Disease: The leaves of monocotyledons appeared to support
sporidia survival.
Secondary Spread of Disease: Seed borne and Soil borne disease
Favourable conditions:
•
•
•
•
•
•
Temperature ranges from 8-23°C
High Soil Moisture (> 15%),
High Nitrogen Dose,
High humidity (>80%),
Close planting favors pathogen attack, and
Cloudiness or rainfall during anthesis favours disease development in
susceptible host varieties.
MANAGEMENT:
• Develop resistant variety viz., WL 1562, HD 2281, etc. Because there are no resistant varieties of
wheat, where Karnal bunt has occurred nonhost crops such as barley, oats or rye may be planted
instead of wheat.
• Use resistant sources like wild species of Aegilops and Triticum, HD 2329, HD 29 and HD 20 for
breeding programme.
• Seed treatment with hot water: Seed soaked in water at 20°C for 5hrs. then in hot water at 49°C for a
minute and again treated with hot water at 52°C for 11minutes.
•
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Cultural practices
Seed should be obtained from healthy area for next season
Crop rotation, Summer ploughing, Green Manuring.
Intercropping with Gram or Lentil.
Mulching with polyethylene can be used to raise soil temperature and reduce teliospore germination.
Planting dates can also be adjusted so that heading does not occur under weather conditions
conducive to infection.
- Follow strict quarantine measures.
- Destruction of affected head.
- Avoiding threshing a diseased crop in the field.
- Controlling irrigation during heading and flowering, deep plowing
- Avoiding use of excessive nitrogen fertilizers.
CHEMICAL METHODS:
• Plant extract of Dhatura stramonium, Thuja spp. can also control hill bunt under field condition
• Treat seed with fungicides like Vitavax, Hexachlorobenzene to control both seed and soil borne
inoculums
• Use of ethyl mercury in seed dressing gives control to the disease with corresponding yield increase.
• Seed treatment with copper carbonate or Thiram@3g/kg seed or Carbendazim (Bavistin) @ 2-2.5
g/kg of seed
• Spray with [email protected]% or [email protected]% or [email protected]% or bitertanol.
• For Karnal Bunt
- Spray tilt @0.1% or Bavistin @ 0.2% at boot leaf stage
- Fumigation of wet soils by Methyl bromide, under plastic cover, reduces teliospores germination by
100%
- Foliar sprays of fungicides may be used to control the airborne inoculum of primary and secondary
sporidia.
Usually, Karnal bunt is difficult to control by conventional methods such as using seed treatment
fungicides and crop rotation. This is because the fungus can survive in a dormant state in the soil for 5
years or more.